Constructing Strong and Tough Polymer Elastomers via Photoreversible Coumarin Dimer Mechanophores

Advanced elastomers with outstanding strength, toughness, and reusability hold significant potential for diverse applications. Using photochemistry and mechanochemistry to develop such materials has become a very effective strategy. Here, we report that photoreversible coumarin-based mechanophores that can make force-/light-triggered cycloreversion are chemically incorporated into polyurethane elastomers to simultaneously enhance their strength and toughness. Coumarin dimer mechanophore cross-linkers are formed in the polyurethane elastomer after exposure to 365 nm irradiation, leading to networks with dramatically enhanced mechanical properties. The tensile strength of the HNA-PU₂₀₀₀ elastomer with coumarin dimer mechanophore cross-linkers could increase from 13.9 to 26.9 MPa, elongation at break from 726 to 1053%, and toughness from 25.6 to 119.7 MJ·m^-3, in contrast to its counterpart HNA-PU₂₀₀₀ elastomer without coumarin dimer mechanophores. Additionally, the polyurethane elastomer exhibits a decent reusable capability via force-/light-triggered cycloreversion of coumarin dimer mechanophores under mechanical stress or 254 nm irradiation. This mechano-/photochemical strategy to improve strength, toughness, and reusable capability of elastomers provides a facile approach for the development of high-performance elastomer materials.